This invention relates to damaged screw removers.
Screws and bolts are very common holding devices, and are often provided with a round head having a transverse slot of generally rectangular cross-section wherein they may be driven by a standard screwdriver. Such a standard screwdriver comprises a blade which has flat sides and a flat bottom, a shank and a handle. The blade fits into the slot of the screw for turning the screw either clockwise or counterclockwise for tightening or removing it. If the screw is exceptionally difficult to turn, or if the screwdriver is worn, damage to the screw slot can occur. If such damage, in the form of deforming the configuration of the slot, occurs when trying to remove the screw, the screw will no longer accept and be turned by a standard screwdriver, presenting a problem in removing the screw.
Barnes U.S. Pat. No. 685,197 discloses a screwdriver which is modified for use with screws having damaged or worn screw slots. The screwdriver of the Barnes Patent has a modified blade including projections extending laterally in opposite directions from the blade, at the lower or working end thereof. The projections are sufficiently sharp to cause them to bite into the wall of the screwhead slot and thereby prevent the tool from slipping out of the slot. The orientation of the projections is provided according to whether the tool is to be used in driving or removing damaged screws. A problem with the Barnes device is that it is sometimes difficult to seat it in the screw slot and establish the biting relationship with the worn or damaged screwhead, and to do so without damaging the device.
Another prior art device is described in Goebel U.S. Pat. No. 4,026,338, which discloses a tool for removing one-way screws. A typical one-way screw has bevelled portions replacing the standard screw slot wall at the areas of engagement for removing the screw, wherein the standard screwdriver will not engage with the screw for removing it. The tool provided for removing such a screw includes a modified blade having pointed, angled projections laterally displaced from the axis of the blade. The projections may be driven into the head of the one-way screw and allow the screw to be removed by turning the tool in the same manner as an ordinary screwdriver.
Other prior art patents include Murphree U.S. Pat. No. 1,547,944, which discloses a broken stud bolt remover, which is essentially a shaped bit adapted to be forced-fit into a guide hole drilled in a broken stud, and Hilsinger U.S. Pat. No. 2,750,821 which shows a damaged screw remover comprising a plurality of spaced-apart points which are driven into a damaged screwhead for engaging it and thereby turning it for removing the screw. Cummaro U.S. Pat. No. 2,815,054 shows a removal tool for damaged Philips-head screws. St-Amour U.S. Pat. No. 4,016,912 shows a modified screwdriver blade for engaging worn screw slots wherein the vertical edges of the blade are enlarged.